Capsule-coated record sheet (with subcoat of latex)

ABSTRACT

THIS INVENTION RELATES TO PRESSURE-SENSITIVE RECORD SHEET MATERIAL INCLUDING A BASE RECORD MATERIAL SHEET HAVING AT LEAST ON ONE SURFACE A SUBCOATING OF LATEX MATERIAL OVER WHICH IS COATED A LAYER OF PRINTING-LIQUID-CONTAINING PRESSURE-COATED SIDE AGAINST A SHEET SENSITIZED TO REACT WITH LIQUID RELEASED BY IMAGING PRINTING PRESSURE MADE AGAINST THE CAPSULE-COATED SHEET TO YIELD A DISTINCTIVELY-COLORED IMAGE. THE LATEX COATING SERVES THE PURPOSE OF CUSHIONING THE CAPSULES AGAINST RUPTURE BY CASUAL PRESSURE OCCURRING IN HANDLING, ROLLING, AND STACKING OF THE SHEET MATERIAL, AND ASSISTS IN THE TRANSFER OF CAPSULE-YIELDED LIQUID TO THE SENSITIZED SHEET BY RESISTING WETTING OF THE CAPSULE-BEARING BASE SHEET BY THE LIQUID RELEASED FROM THE RUPTURED CAPSULES.

United States Patent Olhce 3,565,666 Patented Feb. 23, 1971 U.S. Cl. 11736.2 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates to pressure-sensitive record sheet material including a base record material sheet having at least on one surface a subcoating of latex material over which is coated a layer of printing-liquid-containing pressure-rupturable microcapsules. This sheet is used capsule-coated side against a sheet sensitized to react with liquid released by imaging printing pressure made against the capsule-coated sheet to yield a distinctively-colored image. The latex coating serves the purpose of cushioning the capsules against rupture by casual pressure occurring in handling, rolling, and stacking of the sheet material, and assists in the transfer of capsule-yielded liquid to the sensitized sheet by resisting wetting of the capsule-bearing base sheet by the liquid released from the ruptured capsules.

PRIOR ART Record material sheets coated with mark-forming liquid-containing microcapsules are believed first disclosed in a patent application of Barrett K. Green which issued as United States Pat. No. 2,712,507 on July 5, 1955, and have been in commercial use world-wide since that time with various improved means for keeping the capsules intact against imaging by casually-applied forces. Among these means was the incorporation in the capsule coating of various particle additions of inert matter, such as glass beads and short cellulose fibers, disclosed in United States Pats. Nos. 2,655,453 and 2,711,375, of Robert W. Sandberg, issued Oct. 13, 1953, and June 21, 1955, respectively.

SUMMARY OF THE INVENTION This invention relates to pressure-sensitive record sheet material including a base record material sheet having at least on one surface a subcoating of latex material over which is coated a layer of printing-1iquid-containing pressure-rupturable microcapsules. This sheet is used capsulecoated side against a sheet sensitized to react with liquid released by imaging printing pressure made against the capsule-coated sheet to yield a distinctively-colored image. The latex coating serves the purpose of cushioning the capsules against ruputre by casual pressure occurring in handling, rolling, and stacking of the sheet material, and assists in the transfer of capsule-yielded liquid to the sensitized sheet by resisting wetting of the capsule-bearing base sheet by the liquid released from the ruptured capsules.

The present invention was conceived and developed to control the handling smudge problems which exist Where a capsule-coated sheet is placed against a markreeciving sheet for winding or storage. The smudge is especially pronounced in a paper sheet sensitized with a small amount of acidic-reacting oil-soluble phenolic polymeric material deposited from a solution thereof that leaves, by drying, a highly-sensitive reactive surface film which merely clothes the separate paper fibers, leaving the gross paper structure porous. Such highly-sensitized paper is disclosed in Canadian Pat. No. 768,039, dated Sept. 26, 1967.

While the capsule-bearing sheet of this invention usually is paper of the record material class, any record sheet material can be used as the base to which the latex subcoating may be applied. If highly porous paper is used, a ground coating of film-forming hydrophilic colloid material, such as polyvinyl alcohol, may be applied and then the subcoating of liquid latex applied on top to economize on the materials which otherwise would penetrate the sheet and whose utility would thus be lost.

DETAILED DESCRIPTION The ground coating of polyvinyl alcohol may be applied from a water solution in an amount that will yield a dried weight of 1.1 pounds per ream (25 x 38 inches X 500 sheets) of paper, and the latex is applied thereover as a water dispersion to yield a dried coating weight of 0.5 pound per ream of the same dimension.

If the ground coating is not used, more of the latex material may be applied, the amounts applied being balanced to suit the economic requirements; that is to say, if the base paper sheet is of such quality that the ground coating of hydraphilic colloid is not necessary, then the optimum condition may be attained by using the latex coating by itself. This optimum condition is tested by subjecting the finished sheet to pressure contact against a receiving paper sheet sensitized with 0.25 pound per specified ream of an eligible acidic phenolic resin. The improvement factor test is performed first by the pressures applied by a standard typewriter to estimate the intensity of print, which is directly related to the amount of released capsule liquid that is transferred to the phenolic-sensitized sheet, and, secondly, by smudge tests including a static weight test and a frictional smudge test. The readings of prints made by a typewriter and of smudges produced under static and frictional load are measured as a number Typewriter, Frictional Static,

intensity smudge smudge Without 44 81 81 With 47 97 These are relative numbers; 100 represents no detectable image and the lower the number, the greater the contrast between the imaged area and the receiving sheet background. A significant improvement is noted where the latex coating is used.

The latex material which has proven best and easiest to work with is taken from the synthetic class comprising ethylene-vinyl acetate copolymers, polyvinyl chloride, and polyvinylidene chloride.

The hydrophilic film formers found desirable to use for ease of handling and low cost are the mentioned polyvinyl alcohol and ammonium complexes of casein.

The microcapsules found most useful in practicing the invention preferably are those single oil drop nonclustering kind that are made according to the teaching of Isidore L. Yurkowitz which is disclosed in South African Pat. No. 3,763/67, in which the preferred example is disclosed as follows:

This example concerns the encapsulation of an oil drop having a colorless dye dissolved therein, the capsule wall being formed of a gelatin-gum arabic-polyvinyl methyl ether-maleic anhydride (PVM/MA) copolymer material. Preparation of the system was as follows:

(I) Gelatin solution. grams of high-quality acidextracted pigskin gelatin (Bloom strength-285 to 305 grams, isoelectric pointpH 8 to 9) was dissolved in 890 grams of distilled water at a temperature of 55 degrees centigrade. The pH of this solution was raised to 6.3-6.7 by use of 20 percent, by weight, sodium hydroxide in distilled water.

(II) Gum arabic solution-110 grams of high-quality gum arabic was dissolved in 890 grams of distilled water.

(III) Dye-oil solution.22.5 grams of crystal violet lactone and 18.75 grams of benzoyl leuco methylene blue were dissolved in 972.5 grams of chlorinated biphenyl (biphenyl having 42 percent, by weight, substituted chlorine) and 486.25 grams of refined, essentially parafiinlike, oil (sold as Dispersol-8l515 by Shell Oil Company, New York, N.Y., United States of America), having an initial boiling point of 370 to 400 degrees Fahrenheit and a final boiling point of 450 to 500 degrees Fahrenheit. The system was heated to 90 degrees centigrade to accomplish solution of the dyes.

(IV) Polyvinylmethylether-maleic anhydride (PVM/ MA) copolymer solution.Twenty-three grams of the PVM/MA (such as Gantrez An sold by General Aniline and Film Corporation, New York, N.Y., United States of America, which has a specific viscosity of 1.0 to 1.4 in 1 percent, by weight, ethylmethylketone solution at 25 degrees centigrade, a softening point of 200 to 225 degrees centigrade, and a specific gravity of 1.37) was dissolved in 460 grams of distilled water by being stirred at a temperature of 90 degrees centigrade until the liquid was clear.

(V) Sodium salt of PVM/MA.T the solution of (IV) was added 47 grams of a 20 percent, by weight, aqueous sodium hydroxide solution.

(VI) Gelatin-oil emulsion-In a five-quart Waring Blendor, 925 grams of solution (I) and 507 grams of distilled Water having a temperature of 55 degrees centigrade were blended, at low speed, with 1425 grams of solu tion (III). The addition of (III) required about twenty seconds. Blending was continued for two to three minutes until an average emulsion droplet diameter of three to five microns was obtained.

COACERVATION STEP To 417 grams of the above emulsion were added 136 grams of solution (II) and 447 grams of distilled water in a 1500 milliliter beaker. All components were kept at 55 degrees centigrade, and the beaker was placed in a 57 degree centigrade constant temperature bath. The pH of the liquid system was adjusted to 9.0 with 20 percent, by weight, aqueous sodium hydroxide solution While being agitated.

Phase separation was induced by adding, at a constant rate over ten to fifteen minutes, 13.5 milliliters of a mixture composed of 9 milliliters of solution (IV) and 4.5 milliliters of 14.7 percent, by weight, aqueous solution of acetic acid. The phase separation step was comp eted by addition of 3 milliliters more of 14.7 percent, by weight, aqueous acetic acid and subsequent chilling in an ice bath to below 12 degrees centigrade. While the system was at a temperature below 12 degrees centigrade, 7.5 milliliters of 25 percent, by weight, aqueous glutaraldehyde (pentanedial) was added. The system was allowed to stir for twelve hours while gradually warming to about 25 degrees centigrade, and then 24 milliliters of solution (V) was added drop by drop. The system was stirred for an additional hour, and the pH was raised to 9.810.2 by use of 20 percent, by weight, aqueous sodium hydroxide solution.

The capsule product had a particle size range with a peak at 3.25 microns, 83.8 percent of the particles having diameters of 5.17 microns or less. Inspection of the capsules showed a predominance of single-core entities.

The capsules made by the foregoing procedure, as indicated, were supplied with the colorless chromogenic materials crystal violet lactone and benzoyl leuco methylene blue and were especially made for color development on the acidic mineral attapulgite, which colors the crystal violet lactone blue by an electron donor-acceptor adsorption reaction and colors the benzoyl leuco methylene a blue color by a reaction involving first a hydrolysis fol lowed automatically by an oxidation-reduction reaction. Since the capsule-coated sheet of this invention involves the coloration of the capsule-liquid-receiving sheet by reaction of the capsule contents with acidic phenolic polymeric material which has no coloring activity with respect to benzoyl leuco methylene blue, the latter can be omitted from the capsule liquid contents of the Yurko- Witz type or replaced by an equivalent amount of crystal violet lactone.

Other disclosures for making suitable encapsulations of color-reactant materials which produce capsules useful in the practice of this invention may be found in the following United States patents: No. 2,800,457, of Barrett K. Green et al., No. 2,800,458 (now Re. 24,899), of Barrett K. Green; No. 3,041,288, of William H. Anthony; No. 3,041,289, of Bernard Katchen et al. (clusters); and No. 3,190,837, of Carl Brykno et al.

The various elements involved in the novel sheet construction having been disclosed, examples will now be given of how to make the sheet.

EXAMPLE I As an optional first step, a 30-pounds-per-ream bond sheet of printing paper is coated in any conventional manner with a 5 percent, by weight, concentration of polyvinyl alcohol in water, the polyvinyl alcohol being of 99-100 mole percent hydrolysis, and the aqueous solution of polyvinyl alcohol is applied in amount to yield a dried coating of the specified 1.1 pounds/ream. Where wastage of latex prevails because of paper porosity, the base coating, which resists penetration of the latex, can be used to reduce the total cost of the system. The pounds per ream of base coat used is not a figure that is precisely relevant to the function of the base coating and may vary according to the result desired.

The latex coating is applied as a water dispersion and preferably is of the ethylene-vinyl acetate copolymer type, for economic reasons alone, there being not much choice of one of the specified class over the others as to performance. All latex film coatings of the type specified perform the cushioning function for the capsules coated thereover, but some other latex emulsions have an undesirable efiect on the capsule walls in respect to the ability of the walls to contain liquid contents. The named class of latexes performed in an exemplary manner in respect to their inertness as to aifecting the retention of the capsule contents within the capsule wall material. With this in mind, other latexes may be empirically tested by coating capsules over them and, when dried, trying to extract the capsule contents by a solvent such as toluene--the ineligible latexes being ascertained by the degree of capsule contents extracted. A ten percent rise in the amount of capsule contents extracted over that normally extracted from a capsule-coated sheet of the same standards without the latex subcoating, because of contact with the latex, would render such latex ineligible for use. The ethylene-vinyl acetate copolymer results only in a rise of about four percent increase in capsule con tent extraction and, thus, is well within the limits of ten percent. Latex coatings rating lower than ten percent increase will be deemed eligible for the purpose of practicing this invention even though not specifically named.

With the base-coating film applied, a latex coating having a dried weight of .5 pound per specified ream works admirably with an overcoating of the dried capsules specified.

The capsule coating (dried) should contain about one pound per specified ream of liquid capsule contents when the capsules are made according to the Yurkowitz procedure disclosed in detail above. Said capsules are composed of about to percent liquid contents, of which only between three and four percent is colorless colorable material. The capsules are applied as a liquid slurry of capsules having about 25 percent solids, in water, of which solids 40 percent is capsules and 60 percent is protective solid particles, such as the cellulose fibers mentioned above.

The before-mentioned Canadian Pat. No. 768,039, discloses as colorless color-reactants not only crystal violet lactone as a colorless color reactant which is oil-soluble and reactive with the oil-soluble phenolic polymer sensitized receiving sheet, but many other basic materials having chromogenic groups such as diaryl phthalides; leucauramines; acyl auramines; c p-unsaturated ketones; basic mono-azo dyes; Rhodamine fl-lactams, such as N- (p-nitrophenyl)-Rhodamine fl-lactams; polyaryl carbinols; and 8-methoxy benzoindolinospiropyrans. This capsule coating is applied as a Water slurry over the dried latex coating.

The exact weights and measures of materials are the best now known in yielding a sheet material of high performance against a sheet coated lightly with the solutiondeposit of acid oil-soluble phenolic polymeric material as specified in Canadian Pat. No. 768,039, but it is evident that concentrations, relative weights, and amounts of the significant materials may be varied greatly Without departing from the main thrust of the invention, which is to improve the performance of a capsule-coated record sheet intended to yield for transfer to another sheet the liquid contents of its pressure-rupturable microcapsules by deploying them on a cushion layer of latex film of suitable characteristics, thus preventing casual rupture of the capsules.

What is claimed is:

1. A pressure-sensitive record member comprising a base sheet of paper, a thin latex film layer on a surface of the sheet, and a layer of liquid-containing pressurerupturable microcapsules cushioned by and overlaying the latex film layer, the latex film layer protecting the microcapsules from rupture by casual forces of friction, winding, and stacking but permitting imaging pattern pressure of writing or printing instruments to cause a rupture of correspondingly pressured capsules, and at the same time aiding the transfer of liquid released from the microcapsules to a receiving sheet, and wherein the latex film layer is a dried coat of an aqueous dispersion of polymer material chosen by empirical test such that a toluene-extraction of the liquid contents of the microcapsules on the record member is no greater than ten percent higher than the toluene-extraction of the liquid contents of the microcapsules on a similar record member having no thin latex film layer thereon.

2. The record member of claim 1 having a ground coating of film-forming hydrophilic colloid material between the base sheet and the thin latex film layer.

3. A pressure-sensitive record member comprising a base sheet of paper, a thin latex film layer on a surface of the sheet, and a layer of liquid-containing pressurerupturable microcapsules cushioned by and overlaying the latex film layer, the latex film layer protecting the microcapsules from rupture by casual forces of friction, winding, and stacking but permitting imaging pattern pressure of writing or printing instruments to cause a rupture of correspondingly pressured capsules, and at the same time aiding the transfer of liquid released from the microcapsules to a receiving sheet, and wherein said thin latex film layer is a dried coat of an aqueous dispersion of polymer material selected from the group consisting of ethylene-vinyl acetate copolymer, polyvinyl chloride, and polyvinylidene chloride.

4. The record member of claim 3 wherein the thin latex film layer is a dried coat of an aqueous dispersion of ethylene-vinyl acetate copolymer.

5. The record member of claim 3 having a ground coating of film-forming hydrophilic colloid material between the base sheet and the thin latex film layer.

6. The record member of claim 5 wherein the thin latex film layer is a dried coat of ethylene-vinyl acetate copolymer latex.

References Cited UNITED STATES PATENTS 2,655,453 10/1953 Sandberg 1l7-36.1 2,711,375 6/1955 Sandberg l1736.1 2,885,302 5/1959 Phillpotts 11736.2 3,287,154 11/1966 Haas ll736.2 3,427,180 2/1969 Phillips, Jr. 117-36.2

MURRAY KATZ, Primary Examiner U.S. Cl. X.R. 117-36.4, 76 

